[superguy282]

We recently had a family roadtrip with our 2014 Honda Mobilio 1.5 Petrol. The ODO reads about 76k kms. We enjoyed the entire roadtrip thoroughly and even got a mileage of 15.7kmpl which for 9 year old 7 seater petrol is quite good imho.

However we observed something strange with the handling. Let's say the car is cruising at 80kmph, and comes across road undulations, naturally the car would bounce around a bit before settling down. Whilst driving we observed that at the same speed, the car behaves better and settled quickly at 4th gear rather than 5th. In 5th the car would bounce around for a significantly longer time than at 4th even after the road evened out. The only factor changing between the two is engine rpm which for 5th is 2100 and for 4th is 2900/3000.

This is our first long roadtrip with this car, and I can't tell whether this behaviour was the same since we bought it in 2014. Is this an issue? Or is it how the suspension has been set? Or is it completely natural for a car to do so? We haven't observed this on our previous cars.

[Mr.Boss]

Originally Posted by superguy282

is it completely natural for a car to do so?

Yes, it's normal.

The difference in acceleration torque (in case if the vehicle is accelerating or decelerating) or the driving torque w.r.t change in gear ratio or the engine rpm plays the role in load distribution between front and rear axle and affecting the suspension damping.

[superguy282]

Originally Posted by Mr.Boss

Yes, it's normal.

The difference in acceleration torque (in case if the vehicle is accelerating or decelerating) or the driving torque w.r.t change in gear ratio or the engine rpm plays the role in load distribution between front and rear axle and affecting the suspension damping.

Interesting!

So it would behave even more differently in 3rd gear, acting rear heavy making the steering a touch lighter? Frankly I didn't even think about the torque affecting weight distribution.

[shancz]

I upshift just before a corner which settles down the car a bit and a very slight but flatter cornering also meaning lesser body roll. Downshifting on straights it squats a bit, inherently settling any minor body roll.

Honestly I had never really thought about it until reading this thread

[dhanushs]

3000 rpm will give you more control (throttle) than 2000rpm.

So, I think it's just placebo that you are relating this control to better dynamics.

Originally Posted by Mr.Boss

..The difference in acceleration torque ....

He says he was cruising. And it's a FWD ~100bhp Mobilio.

Originally Posted by superguy282

..Let's say the car is cruising at 80kmph..

[Kosfactor]

Originally Posted by superguy282

However we observed something strange with the handling. Let's say the car is cruising at 80kmph, and comes across road undulations, naturally the car would bounce around a bit before settling down.

Its time for a suspension overhaul

Usually in a city driving condition such things are harmless but one day you take it out on a road trip - fully loaded and that`s where its going to show its age.

[Jeroen]

Originally Posted by Mr.Boss

Yes, it's normal.

The difference in acceleration torque (in case if the vehicle is accelerating or decelerating) or the driving torque w.r.t change in gear ratio or the engine rpm plays the role in load distribution between front and rear axle and affecting the suspension damping.

Originally Posted by dhanushs

So, I think it's just placebo that you are relating this control to better dynamics.


He says he was cruising. And it's a FWD ~100bhp Mobilio.

As pointed out by Dhanesh when you cruise, irrespective of gear, the torque at the wheels are going to be Identical.

I have no idea what could cause such odd behaviour. Get somebody else to drive your car and see if they come to the same conclusion.

Jeroen

[superguy282]

Originally Posted by Jeroen

As pointed out by Dhanesh when you cruise, irrespective of gear, the torque at the wheels are going to be Identical.

I have no idea what could cause such odd behaviour. Get somebody else to drive your car and see if they come to the same conclusion.

Jeroen

It was experienced by both me and my dad, and my brother and mother confirmed that behaviour whilst both of us were driving.

[Jeroen]

Originally Posted by superguy282

It was experienced by both me and my dad, and my brother and mother confirmed that behaviour whilst both of us were driving.

Experience shows it is usually better to have somebody test that is not familiar with your car and or your experiences. The further removed from you, and the most unbiased is the best.

Of course, there may be something wrong with the car. I have never come across such a problem. But then again, I have limited knowledge and experience. Heck, I am not even a car mechanic,

Find a competent mechanic who wants to listen to you and take your car on an extended test drive. You must go along with him/her to point out your concerns.

Good luck will be very interesting to see what causes this

Jeroen

[SmartCat]

Originally Posted by superguy282

Let's say the car is cruising at 80kmph, and comes across road undulations, naturally the car would bounce around a bit before settling down.

Something doesn't add up here. First thing is road undulations are quite rare. Unlikely you will find such a patch of road every 10 km on a highway. So it is not possible to detect the road undulations behavior at different gears and engine RPM, unless you are on some kind of test track.

But then coming to think of it, perhaps you were driving on a less travelled poorly maintained road that had multiple road imperfections.

Whilst driving we observed that at the same speed, the car behaves better and settled quickly at 4th gear rather than 5th. In 5th the car would bounce around for a significantly longer time than at 4th even after the road evened out.

Every road undulation will not be exactly identical. The road undulation that you went through in the 5th gear might have been "deeper" than the previous ones you went through. So the forces acting on the car/suspension will be larger, despite driving at the same speed. That might have caused the car to bounce around for a longer time.

That is, you just happened to be in a particular gear and attributed to car behavior to the gear, rather than how bad the road stretch was.

[vijaysrk]

I have observed the same effect, both in manual cars and in my present AT vehicles(tried using manual mode).

I wonder if the gyroscopic effect of the higher engine RPM on a lower gear has to do with this perceived greater stability.

[Jeroen]

Originally Posted by vijaysrk

I wonder if the gyroscopic effect of the higher engine RPM on a lower gear has to do with this perceived greater stability.

The short answer is no. The long answer below, in certain cases it helps improve dynamic stability!

Obviously, a rotating engine with a flywheel and or converter and gearbox do create some gyroscopic forces. I have observed the same effect, both in manual cars and in my present AT vehicles(tried using manual mode).

A relevant factory is how the engine is mounted. Transverse mounted engines tend to turn in the opposite direction of the wheels as it gives some improvements of handling dynamics.

Obviously on longitudinal mounted engines the gyroscopic force is a complete non factor.

Jeroen

[carthick1000]

This is probably more a subjective observation than actually happening behaviour.

To put that to rest, I would suggest downloading an app like PhyPhox(link) which can help you record a lot of physical quantities like acceleration using just your phone’s internal sensors.

Then drive the same patch of road cruising (constant speed) with 2 different gears and record the acceleration graph (esp. z axis). You can also measure pitch and roll using this app (gyroscope section), but acceleration in z direction is the most interesting one for your query.

Then you can assess for yourself if there is any difference. My suspicion is this is just your perception and not really any change in suspension characteristics.

[superguy282]

Originally Posted by SmartCat

Something doesn't add up here. First thing is road undulations are quite rare. Unlikely you will find such a patch of road every 10 km on a highway. So it is not possible to detect the road undulations behavior at different gears and engine RPM, unless you are on some kind of test track.
But then coming to think of it, perhaps you were driving on a less travelled poorly maintained road that had multiple road imperfections.
Every road undulation will not be exactly identical. The road undulation that you went through in the 5th gear might have been "deeper" than the previous ones you went through. So the forces acting on the car/suspension will be larger, despite driving at the same speed. That might have caused the car to bounce around for a longer time.
That is, you just happened to be in a particular gear and attributed to car behavior to the gear, rather than how bad the road stretch was.

Whilst this could've been a possibility, we observed this mainly on free flowing highways such as the NH4 stretch from Hubbali to Pune. This stretch is quite well made but has a lot of patchwork.

To clarify on what I mean by road undulations, I do not mean a rough gravel or pothole infested surfaces, I meant wherein a flat road isn't truly flat due to patchwork or is wavy if you know what I mean, I can't really explain, but it is definitely present regularly on highways and the response/feel from the vehicle was the same, throughout.

[Sam800]

In a FWD car, when one presses down the accelerator, the back of car pushes down a bit. When same is done in RWD car, the front lifts up a bit.

The job of dampers in suspension is to settle down the vibrations and oscillations of spring.
Now if dampers are starting to get worn out, they will start becoming softer (less effective) or in other case, harder than normal.

We know the coil spring is softest when pressed initially and gets harder progressively (more pressure is required farther down you press).

You drive a long MPV, when you drive in 4th, the torque provided by engine is higher than 5th gear, so is engine braking. The suspension will have 1-2mm of lift or compression depending on wether you accelerate or decelerate, hence the change in handling and settled ride.

Just get your suspensions checked. Any abnormal feel in car probably means there’s some fault somewhere. 75k kms on stock suspension is enough for a MPV. Suspension on my Indigo lasted 55-60k kms only